When Theo Epstein took over as Red Sox GM for the 2003 season, he accumulated a bunch of corner infield/LF/DH types: Giambi, David Ortiz, Kevin Millar, Bill Mueller, replacing everyone who filled those roles in 2002 except Manny Ramirez and Shea Hillenbrand. It was obviously a case of seeing who would stick. Manager Grady Little was mixing and matching for the first couple of months, with Millar, Hillenbrand, and Manny getting most of the starts, but Giambi and Mueller starting more than Ortiz. Millar and Mueller started hot, but Giambi struggled badly. By late May, he was relegated mostly to pinch--hitting, and eventually Hillenbrand was traded to allow Millar, Mueller, and Ortiz (who had been mostly been splitting 1B with Millar and Hillenbrand) to play every day. Giambi got hurt in June, returned for a couple of weeks in July to pinch hit some more, and went back on the DL in early August, never to return to the majors.
It's sad that Jeremy Giambi is remembered mainly as the lesser brother, the guy Jeter caught at home with his flip, and a PED user. RIP.